HELP!!! Bucking and Jerking at cruising speed

[88GTStreetRod]

My car bucks and jerks in 3rd,4th or 5th gear when I try to maintain a steady speed.

I have replaced everything that I can think of, new throtle body, new mass air (cleared up the idle surge), EGR Valve, TPS settings, Idle settings, Idle air control, Fuel presure regulator, oxygen sensors, MSD box, coil, rotor cap, plug wires, spark plugs, You name it, I have looked at it. I am still new at this so I think I have covered my bases. Oh yah, my rpm needle with flickers between 5,000 rpm and 2,000 rpm if I get on it hard. Engine sounds fine, no flickering there, except at cruising speeds.


Please help? any ideas?

 

[5.0Droptop]

Have you replaced the tps Maybe it has dead spots. Some people say they unplug the 10 pin connectors and add dielectric grease and some issues cleared up.

 

[noslow5_0]

i had the exact same problem with my car doing that. Turned out to be my fuel pressure set at 16 psi...... You may want to check urs out again.... just my 2 cents

 

[jrichker]

Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

 

[willys1]

i had the exact same problem with my car doing that. Turned out to be my fuel pressure set at 16 psi...... You may want to check urs out again.... just my 2 cents

Dude,did you get that other TB ?

 

[IndyBlk5.0]

sounds like a fuel problem... do you have a AFPR? if not, you could always go to autozone and buy a fuel pressure checker and check it with the shrader valve on your fuel rail, then stick that puppy back in the box and return it =) hehehehe

 

[88GTStreetRod]

Did you lower the 16PSI and it worked or thats what it was set at?

i had the exact same problem with my car doing that. Turned out to be my fuel pressure set at 16 psi...... You may want to check urs out again.... just my 2 cents

 

[88GTStreetRod]

The TPS is brand new, do you think I could have a problem with a new one? I will try anything. I have dumped $4K into this car in the last month. If i do not get it running right, I may be forced to light it on fire!

Have you replaced the tps Maybe it has dead spots. Some people say they unplug the 10 pin connectors and add dielectric grease and some issues cleared up.

 

[88GTStreetRod]

The only codes that I received when hooked up, was computer failer. However, the instructions said if the battery was recently disconected then ignore. I had the battery disconnected before hand. No other error codes appeared.

Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

 

[IndyBlk5.0]

what is your fuel pressure at streetrod? it would help if you gave us what pound your injectors you have, and any major modifications. that way we could tell you what psi your supposed to be running around.. if you dont have a fuel pressure gauge and you mess with a afpr, its impossible to really have any idea what your running at... i was running at about 65 psi one time becuase i didnt have a gauge.

 

[88GTStreetRod]

Fuel presuare was at 38 and just moved up to 42 to try it. I have has it down to 30 also. I have 24lb injectors with a BBK fuel regulator and 155lb fuel pump. I have Edelbrock Performer RPM II upper and lower intake with Edelbrock Performer RPM heads. I was told by previous owner that car has a E303 cam, but it hits harder than others that I have heard. I have the underdrive pullys, 70mm Throtel Body, 75mm Mass Air, Cold air induction (Fenderwell) MSD box, Accel Coil, etc.... Just put the heads and intake, throtel body on, and started having this problem.

what is your fuel pressure at streetrod? it would help if you gave us what pound your injectors you have, if you have a apr, and any major modifications. that way we could tell you what psi your supposed to be running around

 

[IndyBlk5.0]

ok fuel pressure doesnt seem to be the issue if it did it under all those situations... next thing to look for is any vacume leak you may be having. check all your vacume hoses.

 

[88GTStreetRod]

I have checked every hose imaginable. I may not be listening or looking for the right thing. I would thing I would hear a loss of air noise correct?

ok fuel pressure doesnt seem to be the issue if it did it under all those situations... next thing to look for is any vacume leak you may be having. check all your vacume hoses.

 

[IndyBlk5.0]

correct, ussually if you have a vacume leak you will hear a hiss sound. you see. i never had the problem until i messed with my timing and fuel pressure, that was when it started bucking on me... check timing?

 

[88GTStreetRod]

I have had the timming from 8 degrees to 14 degress. It is currently set at 12.5 degrees. The car runs great wide open and as long as you give it gas. When it bucks, it feels like someone is turning the gas off and on. What do you think about running the fuel presure down to 20lbs? Too lean? It runs the best at 35psi, but I am afraid to run it too low incase it burns a hole in a piston.

correct, ussually if you have a vacume leak you will hear a hiss sound. you see. i never had the problem until i messed with my timing and fuel pressure, that was when it started bucking on me... check timing?

 

[88GTStreetRod]

Yah, bought new throtel body and Mass air. The new mass air cleared up my idle problems

Dude,did you get that other TB ?

 

[IndyBlk5.0]

20 is too low especially with your setup... did the problem get any worse or better when you messed with the fuel pressure?

 

[88GTStreetRod]

Just got back from a run. Actually got worse at 42psi, ran the best at 35 psi. Go figure. I hooked a manual gage up to see if my BBK gauge was working ok., it is working ok.

20 is too low especially with your setup... did the problem get any worse or better when you messed with the fuel pressure?

 

[IndyBlk5.0]

your new mass air meter is calibrated for 24 pound injectors correct?

 

[SR86]

I had a problem with my 5.0L, would buck and jerk at anything but WOT, changed EVERYTHING, starting with the TPS,down to 02 but to no avail, it turned out to be a bad TFI, which usually just have heat soak failure..swapped in an old spare, no more problems...was that ever agrivating..